Hollywood often portrays aliens as human-like bipeds such as “Star Trek's” Mr. Spock, played by Leonard Nimoy. But scientists say if living creatures exist beyond Earth, it's doubtful they will resemble us. (Getty Images/Bertil Unger)

Recent discoveries have given renewed prominence to the search for intelligent life beyond Earth, including dramatic new evidence Mars once had water. NASA is already planning more missions similar to the current $1 billion exploration of the Red Planet by unmanned rovers. And President Bush recently proposed establishing a base on the moon to prepare for an eventual manned mission to Mars. While NASA will be looking for microbial life, the chance that evidence of an intelligent civilization might show up has not been dismissed. Critics of the search for extraterrestrial intelligence (SETI) say the money being spent on research should be used for more promising projects. But supporters argue that even if the search fails, it may lead to spin-off benefits for all humankind.